1. Field of the Invention
This invention relates to receiving sheets used for dye transfer type thermal printing using a printing means, for example, a thermal head, an optical head for laser beam, etc., or a current-applied head. And it relates particularly to receiving sheets useful for high-speed printing and/or relative-speeds printing in which printing is conducted while controlling the relative speeds of a transfer sheet and a receiving sheet so as to make them different from each other.
2. Description of the Prior Art
In dye transfer type thermal printing, a sublimable dye on a transfer sheet is transferred to the dyeable layer of a receiving sheet to form an image. As resins constituting the dyeable layer of the receiving sheet used for the dye transfer type thermal printing, there are known various thermoplastic resins and various thermosetting resins [for example, Jap. Pat. Appln. Kokai (Laid-Open) Nos. 58-212994 and 60-25793]. In general, saturated polyester resins have a high dye-affinity and hence have been sufficiently investigated. When used alone, they involve a problem of their fusion to a transfer sheet (a color sheet). Therefore, it has been proposed to prevent the fusion by crosslinking such a high-dye-affinity resin by the use of an isocyanate or by incorporating the same with a reactive silicone oil [for example, Jap. Pat. Appln. Nos. 60-34898, 61-132387 and 63-19295].
Thermosetting resins which have a high heat resistance are useful for high-speed printing. Heretofore proposed radical- or ionic-polymerization resins undergo inhibition of curing, by oxygen, water or the like in the air during curing, resulting in formation of an uncured portion in the surface of a dyeable layer. The unreacted resin remains in the uncured portion and reacts with dyes and the like to lower the reliability. This problem is serious because an image is printed in the surface portion of the dyable layer. In addition, it is preferable to use resins having dye-affinity for both low-speed printing and high-speed printing by varying their heat resistance. However, in the case of various heretofore proposed resins, it is not easy to vary the heat resistance of their cured products widely while maintaining the above reliability. Thermosetting resins requiring a crosslinking agent such as isocyanate which becomes a constituent of their cured products, are disadvantageous in that since the degree of crosslinking of the cured product is closely related to the printing sensitivity, the degree of crosslinking should be controlled by adjusting the amount of the crosslinking agent. Relative-speeds printing requires a dyeable layer having an excellent surface slipperiness. As resins constituting the dyeable layer, resins capable of imparting properties such as excellent surface mold release properties and surface slipperiness are preferable. Heretofore proposed resins hardly impart such excellent properties, and no satisfactory resin has been proposed.